It's at the end of its lifespan (USUM are confirmed to be the last Pokémon games on the 3DS for example) and being replaced by the Switch essentially due to no proper handheld-only-successor in plans.

Even if we were in 2015 or something, starting development of a new game would just be the same mistake as Dark Dawn all over again... a game that had to be reinvented to adapt to the new hardware, just as said hardware is dying out, preventing extremely convenient re-use of the resources for at least another sequel to complement it a few years later, leaving us with a single entry that clearly feels complete but is forced to stand on its own at the same time.

Nintendo America President Reggie Fils-Aime confirmed that the company plans to support the 3DS beyond 2018. with Pokemen and Metroid being pumped out late 2017, theres no reason why they would try and shove a possibly failing title into the dying niche of the 3ds. the systems are portable so its be much easier to remake the 3ds onto the switch of the wii u unlike the gba and the ds. still hope i haz.

I thought so for quite a while as well (and usually got overrun by some Switchfanboys and 3DS doomsayers).. but given my interest in PKMN, I know that throughout the years Gamefreak/TPCi said more than once that the core-series would never leave the handhelds for a move to consoles. But with the Switch situation we now know that the PKMN-devs have abandoned the 3DS and are currently completely focused on making the next PKMN title for the Switch, which made me realize that there is not a true 3DS-successor in plans in near future.

Otherwise Gamefreak specifically would be waiting it out rather than jumping ship like they have no other option.

Unless Nintendo was keeping a 3DS successor secret to developers of that caliber...which would be amazingly dumb. From recent interviews of Gamefreak you even get the feeling that they're fearing huge disappointment and risk for going to the Switch (as people are coming up with baseless ridiculous expectations), and that they just wanna make more PKMN games like they've always done.